Electrical heating device



Aug. 3, 1943. F. BLACK ETAL 2,325,585

ELECTRICAL HEATING DEVICE Filed Sept. 25,, 1942 2 Sheets-Sheet 1 FIG I F l G .2.

LAWRENCE F. BLACK CLARENCE H.MELLOR Gum;

Aug. 3, 1943.

L. F. BLACK ET AL ELECTRICAL HEATING DEVICE Filed Sept. 25, 1942 FIGJZ:

llllllll. Illmm. mum. ullllllllv 2 Sheets-Sheet 2 I LAWRENCE F.8LACK CLARENCE H. MELLOR Patented Aug. 3, 1943 ELECTRICAL HEATING DEVICE Lawrence F. Black, United States Army, and Clarence H. Mellor, United States Army, Denver, Colo.

Application September 25, 1942, Serial No. 459,617

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3790. G. 757) 13 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without payment to us of any royalty thereon.

This invention relates to an apparatus for heating by electricity and more particularly to an electrical induction heater for small metal parts such as soldering irons and the like.

While devices for heating small metal parts such as soldering irons, rivets, etc., are well known in the patented art, such devices generally' require either a flame source of heat or, if

electrical, generally require the use of a'heatradiating element employing a comparatively high resistancehonductor. Either of these two modes of heating, i. e., flame source or electrical resistance element, is comparatively expensive to operate if kept hot all of the time, and, alternatively, if they are allowed to cool and then are restarted each time that a particular article is to be heated, they necessarily take a certain amount of time to reach anoperating temperature. By our device, we eliminate the need for a flame source of heat 'and,'at the same time, utilize electricity as the heating medium without employing an electrical resistance unit to supply the. heat externally to the object being heated. Furthermore, although our device stands ready for operation whenever the primary circuit is energized, it draws a substantial electric current only when the part to be heated is inserted into the secondary circuit. Another advantage isthe elimination of switches since the insertion of the part to be heated brings our device into operation and its withdrawal causes the device to cease operation.

Accordingly, it is an object of the present invention to provide an apparatus for electrically heating small metal parts, such as soldering irons and the like.

Another object of the present'invention is to provide an electrical heating apparatus for small metal parts such as soldering irons and the like which eliminates the necessity of using an-open flame and which is fast, eflicient and inexpensive in operation.

Another object of the present invention is to provide an electrical inductionhater for small metal parts-such as s ldering irons and the like which, although connected to an electrical circuit, remains normally inoperative until the part or parts to be heated are inserted into the secondary circuit of the induction heater device.

Another object of the present invention is to provide aninduction'heater for small metal parts such as soldering irons and the like which comprises a closed core transformer having a primary circuit and a closed secondary circuit so arranged that substantially no current flows in the secondarycircuit until the part to be heated is inserted into said secondary circuit.

These and other objects of our invention will become apparent from the following detailed description taken in conjunction with the accompanying. drawings and the invention will be pointed out with particularity in the claims appended hereto.

In the drawings:

Fig. l is a front view of an embodiment of our invention;

Fig. 2 is an end view of the'embodiment shown in Fig. l. I v

Fig. 3 is a sectional view taken on line 3-3 of Fig. 4 is a sectional view taken on line 4-4 of Fig. 1.

Fig. 5 is a perspective view of a soldering iron adapted for use with our invention.

Fig. 6 is a perspective view of a solder ladle suitable for use with our invention.

Fig. '7 is a perspective view of the embodiment of our invention disclosed in Fig. 1 with a soldering iron mounted in heating position.

Fig. 8 is an end view of another embodiment of our invention.

Fig. 9 is a sectional view taken on line 9-9 of Fig. 8.

of our invention.

Fig. 11 is anend view of a modification of the mounted to surround a portion of the periphery of a closed core l2 made of laminated magnetic metal such as silicon steel stampings or similar suitable material. Core I2 is formed from a series of interleaved right-angled shaped stampings l3 and H which act, in a manner well known in the art, to reduce eddy current loss. Surrounding core l2 is asecondary winding 15 which is preferably made in the form of a con- Fig. 10 is an end view of another embodiment tinuous loop of metal having good electrical conductivity such as copper or aluminum and which is mounted so that it entirely surrounds core i2. As will be seen from the drawings, secondary l5 is formed in modified ellipse shape so that the long sides are substantially straight and the short connecting ends are curved", thereby giving the appearance of a race track. We define this figure as mixtilinear and hereinafter .When the word mixtilinear figure is used we intend it -to mean a figure resembling an ordinary race track in general appearance. The secondary l5 has in each parallel straight side of the mixtilinear loop member a plurality of aligned openings l6 adapted to receive the part'or parts to be' of substantially the same configuration and diameter as that of the individual orifices H5. The secondary member I5 is preferably mounted adjacent leg l2d of the transformer core l2 oppositeleg [2a upon which the primary coil it is mounted. In this position secondary' l5 surrounds, in a single loop of mixtilinear form, the two legs I2?) and I of the transformer core i2 which are substantially at right angles to the leg l2a upon which the primary coil is mounted Also, the axis of the secondary I5 is substantially at right angles to the axis of the primary coil l0. While the manner of supporting the secondary winding i5 is not shown, it will be understood that it is supported to surround core l2 by means which insula'te' it from said core.

A soldering iron and a solder ladle suitable for use with our invention are disclosed in Figs. 5 and 6. Referring to Fig. 5, the soldering iron comprises a head I'd, preferably made of copper although other electrical conducting materals may be used, a wire l8 and a'handle l9, the latter being made of wood or.some other suitable heat insulating material. the solder ladle comprises a ladle cup 20, preferably made of copper or similar suitable electrical conducting material, a stem H and a handle 22.

Referring to Fig. '7, it will be seen that the mixtilinear secondary l5 is-disclosed as having a part to be heated, in this case a-soldering iron of the typedisclosed in Fig. 5, thrust into a pair of the openings It so that member I! constitutes a bridge between the straight parallel sides of secondary l5 and forms two complete electrical circuits surrounding legs lb and l2 c of core l2.

The actual'bridging by member I] is moreclearly shown in the dotted line portion of Fig. 4'. Member II is so formed that it fits into opening it se curely and forms a good electrical contact, yet it can be withdrawn quickly. Th manner in ,which member i1 is heated is. explainedhereafter.

Figs. 8 and 9 disclose another embodiment of Y our invention in which the transformer secondary is modified in shape, although still retaining Referring to Fig. 6,

closed a primary coil i ll, mounted on a laminated magnetic core i2, and a secondary winding 25.

Secondary is formed from a bar of material having a high electrical conductivity such as copper or aluminum, saidbar being provided at the center portion thereof with a protuberance 26, of the same width asthe bar, having a curved face 26a formed therein. The ends of the bar are then bent around as shown at 29 to form a loop surrounding the magnetic core [2 and extending through the air space surrounded by core i2..to form an opening 27, bound partially by Fig. 10 discloses another embodiment of our invention, similar to the embodiment disclosed in Figs. 8 and 9, in which the secondary winding 25 is of continuous loop or mixtilinear form, similar to that shown in Fig. 7, and has attached thereto members 26 and SI, of the same width as member 25, which have .oppositely disposed curved faces 26a and 3m forming opening 21 into which the part to be heated is inserted. Members 26 and 3| are attached to secondary winding 25 by means of bolts 32 or'similar suitable holding means. Since member 3! extends through the air space surrounded by core I 2,

opening 21 is so located that the part being heated need not be inserted into said air space. Members 26 and 3| are made of the same material as member 25, namely, a good electrical conductor such as copper or aluminum bus-bar.

In Fig. 11 we have disclosed a modification of the embodiment of our invention shown in Figs. 8

and 9 in which the secondary winding 25 of substantially mixtilin'ear form is formed with a plurality of openings 21 adapted to receive several parts to be heated at the same time. In this construction the secondary member 25 has additional members 53, of the same width and material as member 25, connected thereto, said members being suitably bolted by bolts 30 or otherwise attached to member 25 to form the construction shown in Fig. 11. Likewise, the main bodyof secondary winding 25 has formed thereon a sries of protuberances 26 which have curved faces 26a thereon matching the curved faces, 25a and 33a, on the ends of members 25 and 33 to form a series of generally circular openings 21.

Likewise Fig. 12 is a modification of the embodiment of our invention disclosed in Fig. 10 in which a plurality of openings 21 are provided so that several articles can be heated simultaneously. A plurality of members 26 and a plurality of members 3i are matched, curved faces 26a its general mixtilinear appearance, to permit the' insertion of'a part to be heated without extendingthe part into.th space surrounded by the magnetic core. Referring to Fig. 8, there is disand am being opposite each other for each pair, and attached by bolts-32 to form a series of openin s 21.

The operation of our invention is as follows:

With the primary winding connected to a suitable source of alternating electric current, such as the standard 60 cycle current, a pulsating magnetic flux will be set up in the magnetic core member of the transformer. As shown in Fig. 13, at a given instant, the primary current Ip will causethe magnetic flux pulsation (p in the direction indicated in Fig 13. This flux pulsation will have opposite directions in opposite legs 35?) and 350 of the transformer core 35. Consequently in that portion of the mixtilinear secondary loop 36 adjacent leg 3% of the transformer core 35 there will be a voltage induced which will be of opposite polarityto the voltage induced in that porti'on'o'f the secondary loop 35 adjacent leg 350 of the transformer core 35 with the result that substantially no current flow will'take place in thetransiormer secondary. Secondary 36 thus transforms the magnetic flux pulsations concentrated in core 35 into components of electrical energy which are substantially equal and opposite in direction thus creating a source of energy which is, so to speak, held in leash and which can be aptly described as potential electrical energy. Since the voltages induced in secondary 38 are of opposite polarity we refer to the substantially equal components of potentia1 lectrical energy as being of opposite polarity. As the primary current lip alternates, the magnetic flux (p will also alternate but, at each instant, the voltages induced in those portions of the secondary winding 35 ad,- jacent legs 35b and 350 of the transformer core will be of opposite polarity and consequently any secondary current Is that flows will be due to the'unbalanced resistance of the circuit which, for practical purposes, is negligible. However,

if a conducting member 31, shown in Fig. 14, is

inserted into the secondary circuit 36 between thoseportions of said circuit adjacent opposite legs 35b and 350 of the transformer core 35, two

closed loops, or short-circuited secondary loops,

are formed with .the result'that large amounts of current will flow through the short-circuiting member 31 in both directions, as the current alternates, thereby heating it.. Thus member 31 forms a common flow path for the secondary current flowing ineach of said closed loops about legs 35b and 350 of core member 35. This is substantially what happens when a metal part, such as a soldering iron head made of copper or other conducting material, is inserted through the openings l5, as shown in' Fig. '7 or through the openings 27 shownin Figs. 8 and Ill-'12.

With several'metal short-circuiting members inserted in the secondary there will merely be a number of parallel circuits formed and the d'e-. vice .will operate. even though more than one metal part, such as a soldering iron, is being- The addition of the heated at the sametime. short-circuiting member 31 thus releases the energy which is normally held in check because of the opposite'polarity or bucking direction of the two energy components. Once released the potential energy becomes kinetic and continues to be kinetic as long as the member 31 remains our device'forms 'a part of the secondary circuit, electrical current flowing in said secondary circuit will pass through said article and the dissipation of electrical power as heat in said article Will be controlled by the magnitude of the electrical current passing through it and the resistance 'of said article to the current flow.

- The power loss, as heat, in said article is ex= in position. A large portion of the energy is dissipated as heat in the shorting member 31.

The apparatus comprising our invention can be left plugged into the line, i. with the primary circuit connected to a suitable source of alternatingelectric current, Without being unduly expensive. from an operating standpoint. Thisis so because our device draws substantial amounts of electric current only whenthe part to be "heatedshort circuits the secondary member. At other times it acts substantially as if the transformer were open circuited with the consequent result that the only current drawn from the line at' these times is the exciting current of the transformerdevice which forms but a small percent of the'totalpower requirement. Since the particular article being heated by pressed by the well Known Equation 1 R where I is the current flowing in the article, generally expressed in ampere units and R is resistance of the articleto current flow, generally expressed in ohms. Since efficient utilization of our heating device demands that the heat be localized in the article being heated, it is desirable that the part being heated, if it is composed of material having substantially the same electrical conductivity as the rest of the secondary circuit, have a higher resistance to current flow per 'unit area cross-section than the rest of the secondary circuit. Where the materials have substantially the same electrical conductivity, this isaccomplished by heating articles which have a smaller cross-sectional area than the remainder of the secondary circuit.

Although optimum results are achieved with the foregoing set-up, the heating of articles of larger cross-section than the remainder of the secondary circuit can be accomplished but, if the materials comprising the secondary circuit have substantially the same electrical conductivity, a longer heating period is required and the heating of the secondary circuit exclusive of the inserted article will be greater. It will be .obvious that there is practical limit to the crosssectional area of the article being heated, depending upon the size of the rest of the secondary circuit and the comparative resistance per unit .area of the two, beyond which one cannot go without overheating the rest of the secondary circuit. The permissible range of cross sectional areas of the part being heated will readily be arrived at by one skilled in the art.

Where the resistance of the part being heated to electric current flow is materially different from that of the remainder of the secondary circuit, heating can nevertheless be accomplished as long as said variance is not so great as to prevent effective current flow in the secondary circuit or, at the other extreme, to prevent the localization of heat in the part being heated due to the extremely low resistance of said part as compared to the rest of the secondary circuit. The permissible variance will be readily apparent to one skilled in the art. Since the secondary loop into Which'the part to be heated is inserted will be made of material having a high electrical conductivity, such as copper or aluminum, any variation in resistance between the article being heated and the rest of the circuit will generally be caused by the higher resistance of said article.

" Whether the part being heated is made of the ofljoperation of our device, we insert a copper so dering iron heador a copper solder ladle into a copper bus-bar secondary circuit having a greater cross-sectional area than either the copper soldering iron head or the copper solder ladle.

the openings in one side being in-alinement with r the openings in the other side, whereby an article heating soldering irons having a head made of copper or material of like electrical conducting properties, or for heating other small metal parts which are electrically conductive. Furthermore, our device does not utilize an' open flame, stands ready for use at any time so long as the primary circuit is plugged in, and develops an intense heat within a relatively short time. The insertion of the part to be heated starts the device into operation and the withdrawal of the heated part causes it to cease operation.

While we have described several particular embodiments of our invention, it is to be understood that we do not wish to be restricted thereto, and that we intend to cover all modifications thereof which would be apparent to one skilled in the art and which. come within the spirit and scope of the appended claims.

Having thus described our invention, what we claim as new and wish to secure by Letters Pat- I ent is:

1. An electrical heating device comprising a closed magnetic core, a primary winding surrounding a-portion of said core, anda closed secondary winding entirely encircling said core, the axis of said secondary winding being substantially at right angles to the axis of said primary winding and lying in the medial plane of the core of said closed magnetic core.

2 An electrical heating device comprising a closed magnetic core, a primary winding surrounding a portion of the periphery of said core, a closed secondary winding entirely encircling said core and symmetrically disposed with respect thereto, the axis of said secondary winding being substantially at right angles to the axis of said primary winding, and lying in the medial plane of the core of said closed magnetic core, and means located in said secondary winding adapted to receive articles to be heated.

3. An electrical heating device comprising a closed magnetic core, a primary winding surrounding a portion of the periphery of said core, and a closed secondary winding entirely encircling said core and symmetrically disposed with respect thereto, the axis of said secondary winding being substantially at right angles to theaxis of the primary winding and lying in the medial plane of the core of said closed magnetic core, and said secondary winding having openings therein adapted to receive articles to be heated.

4. An induction heater comprising a closed magnetic core, a primary winding surrounding a portion of the periphery of said core, a closed secondary winding entirely encircling said core and symmetrically disposed with respect thereto,

' the axis of said secondary winding being substantially at right angles to the axis of the primary winding, said secondary winding being mixtilinear in shape and having openings in each of the long sides thereof, said openings in one side being in alinement with the openings in the other side whereby an article to beheated may be inserted into said alined openings to form a closed secondary circuit surrounding a portion of the magnetic core. 5. In an induction heater, a secondary winding comprising a closed loop of material having a high electrical conductivity, said secondary winding being mixtilinear in shape and having openings located in each of the long sides thereof,

' tuberances attached thereto facing the interior forming the other long side of said secondary,---

to be heated can be inserted in a pair of said openings to form a bridging circuit between-the long sides of said mixtilinear secondary.

6. In an induction heater, a closed secondary winding comprising a copper bus-bar of mixtilinear form having openings located in each of the long sides thereof, the openings in one side being in alinement with the openingsin the other side, whereby an article to be heated canbe inserted in a pair of said openings to form a bridging circuit between the long sidesof said mixtilinear secondary.

7. An electrical heating device comprising a closed. magnetic core, a primary winding surrounding a portion of the periphery of said core, and a closed secondary winding entirely encircling said core and symmetrically disposed with respect thereto, the axis of said secondary winding being substantially at right angles to the axis of said primary winding and said secondary winding being formed of mixtilinear shape and respect thereto, the axis of said secondary wind-- ing being substantially at right angles to the axis of said primary winding and said secondary winding being mixtilinear in shape and including a substantially straight conductor portion forming one of the long sides of said secondary, said straight conductor portion having proof the secondary, the ends of said protuberances having curved faces formed therein, and a plurality of connected curved conductor portions forming the other long side of said secondary. theends, of said curved portions extending toward the interior of said secondary to a line adjacent the ends of the protuberances attached to the straight conductor portion, and said curved portion ends having curved faces formed therein located opposite the curved faces formed in the ends of the protuberances attached to the straight conductor portion to form .a receiving means for articles to be heated.

- 9. In an induction heater, a closed secondary winding of substantially mixtilinear shape, said secondary being formed from material having a high electrical conductivity, and said secondary including a substantially straight conductor portion forming one of the long sides of said secondary and a plurality of connected curved conductor portions forming the other long side of said secondary.

10. In an induction heater, a substantially mixtilinear shaped closed secondary winding of material having a high electrical conductivity comprising, a substantially straight conductor portion forming one of the long sides of said secondary, said straight portion having protuberances attached thereto facing the interior of the secondary, the ends of said protuberances' having cur/"ed faces formed therein, and a plurality of connected curved conducting members the ends of said curved portions extending torespect thereto, the axis of said secondary winding being substantially at right angles to the axis of the primary winding, and said secondary winding beingmixtilinear in shape and including a plurality of protuberances attached to the long sides of said secondary, the protuberances on one side of said secondary winding being in alinement with those on the other side thereof and both sets of protuberances extending toward the interior of the secondary winding to dispose their extremities in adjacent relation.

12. An electrical heating device comprising a closed magnetic core, a primary winding surrounding a portion of the periphery of said core,

and a closed secondary winding entirely encircling said core and symmetrically disposed with respect thereto, the axis of said secondary winding being substantially at right angles to the axis of the primary winding, and said secondary Winding being mixtilinear in shape and including a plurality of protuberances attached to the long sides of said secondary, the protuberances on one side being in alinement with the protuberances on the other side and both sets of protuberances extending toward the interior of the secondary so that their ends are adjacent, and curved faces formed in the ends of the protuberances to form a receiving means for articles to be heated.

13. In an induction heater, a closed mixtilinear shaped secondary winding of material having a high electrical conductivity, said secondary having a plurality of protuberances attached to each of the long sides thereof and said protuberances facing the interiorof the secondary, the protuberances on one side being in alinement with the protuberances on the other side so that their ends are adjacent, and said ends having curved faces formed therein to form openings adapted to receive articles to be heated.

LAWRENCE F. BLACK. CLARENCE H. MELLOR. 

